A publication of the National Electronics Manufacturing Center of Excellence June 2003

EMPF Director

Michael D. Frederickson
mfrederickson@aciusa.org


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MEMS IMU
E
ver-increasing DoD technology demands in guided munitions require electronic hardware to survive and function normally at over 15,000 g's. Examples of such stringent demands can be found with the emerging precision guided munitions (PGMs) such as the Navy's Extended Range Guided Munition (ERGM) and the Army's Excalibur. Demands such as these push the limits of the sensors, electronics, and packaging that comprise the hardware, thus requiring technical development efforts to establish proven sensors and packaging techniques able to meet DoD needs.

An enabling condition for precision-guided munitions is the ability of the electronics packaging to survive the associated high-g environments (>15,000 g's). Future applications for the Advanced Gun System [AGS] and the 105mm and 120mm rounds for the Future Combat System [FCS] will see high-g environments in excess of 20,000 g's. In addition, reduced size packaging will enable next generation guidance electronics such as the Deeply Integrated Guidance /Navigation Unit (DIGNU), which combines the Inertial Measurement Unit (IMU) and the GPS receiver into one four to five cubic inch unit. Achieving smaller, gun-hardened electronic systems can also enable new classes of guided weapons such as Helicopter fired missiles. The need for the high-g survivability, along with the ever-increasing demand for higher performance and smaller electronics systems in PGMs, presents the need to establish and demonstrate electronics packaging guidelines for gun-hardened applications. Beyond control electronics is the DoD need for micro-electronic packaging that can be utilized in new fuze programs (MOFA, MFF, HTSF to name a few) and seekers and sensors for missiles.

One emerging PGM is the U.S. Navy ERGM. The ERGM round will be fired from a gun barrel on a Navy ship and have superior target accuracy over a significant distance. The round will be guided by the Global Positioning System (GPS); however, a form of inertial guidance (inertial meaning functions without external reference or communication), known as an inertial measurement unit (IMU) is also necessary in case of GPS jamming, or times when the GPS signal cannot be acquired. The enabling path to producing functional, gun-hardened IMUs at a reasonable cost is to use IMUs based on Micro Electro-mechanical system (MEMS) technology. MEMS technology typically refers to small mechanical elements micro-machined into a silicon substrate, which also contains circuitry. American Competitiveness Institute is involved with a Navy Manufacturing Technology program to produce low-cost IMUs for precision guided munitions applications (Figure 1).

The Navy MANTECH program will focus on driving cost out of the MEMS sensor fabrication, circuit cards, and calibration time of the IMU. The IMU will also be expected to survive the gun shock, which can be in the neighborhood of 15,000 g's.

The L-3 µSCIRAS IMU demonstrates the current level of technology of MEMS IMUs. The Navy, Army, and Air Force have already committed funds to industry to develop the next generation of MEMS IMUs. These IMUs are expected to be smaller, cheaper, and even more accurate. Additional activity is looking at ways of integrating the GPS receiver into the IMU housing. This unit is termed DIGNU for Deeply Integrated Guidance and Navigation Unit. Success in programs such as these would open up new opportunities for IMUs not only for weapon systems such as Helicopter fired rounds, but also for applications such as underwater vehicles.

As part of the effort to manufacture gun-hardened IMUs and related PGM electronics, ACI is developing a method of packaging gun hardened electronics based on high-g test data. This information can be used by numerous DoD manufacturers that make subsystems such as IMUs, GPS receivers, SAASMs, fuses, and control electronics. ACI is selecting, assembling,and test packaging interconnection approaches not currently proven in high-g applications that provide a definable benefit in terms of high-g survivability, size reduction, and/or cost. ACI can leverage its current involvement in the MEMS IMU area as well as its internal packaging capability, knowledge, and industry contacts. The work performed here would establish failure mechanisms of packaging currently being tested in high-g electronics such as wire bonding and flip-chip. Further investigation can include more advanced packaging approaches for consideration that would enable size reduction such as 3-D chip stacking, stud-bumping of MEMS, or use of a folded flex-rigid circuit board.

The selected packages would be assembled into test articles on ACI's demonstration factory floor. The test articles would be tested off-site at an established high-g testing facility. ACI would use its in-house testing and analysis equipment to perform functional check-out and any associated failure analysis. In addition to the high-g survivability data, ACI would include in the Handbook the corresponding manufacturing guidelines for package assembly.

From this critical packaging design data, ACI can establish guidelines for gun-hardened electronics would allow all the manufacturers of high-g systems and subsystems to draw from a single source of packaging information. This would prevent redundancy of the development effort and provide the DoD industrial base a verified and tested design base from which to answer the DoD requirements. In addition, having high-g data for packaging would provide a basis of confidence that a packaging approach has merit and should be investigated further as next generation products are developed. In the end, this would not only contribute to the fielding of current and next generation PGMs, but it would do so with an emphasis on low cost, manufacturable packaging solutions.

The level of investment from multiple DoD branches demonstrates the current interest in precision guided munitions. Through the efforts of ACI and programs such as Navy MANTECH, the gun-hardened electronics technology can become not just available, but affordable to meet the Battlefield needs of today and tomorrow.


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